Integrated aspheric optical coupler for RF planarized automatic photonics packaging

Abstract

The invention relates to an optical, integrated alignment device for accurately aligning and efficiently coupling energy between in-plane optical devices. A semiconductor substrate is etched to include a groove for an optical fiber and a lens for passing an optical signal from a cut fiber to a photodetector. The etched semiconductor substrate may be used to pass an optical signal from a surface light emitting device to a cut fiber. The end of the optical fiber is cut at a slant that redirects an optical signal from the fiber through the lens or vice-versa. The lens focuses the optical signal onto a target.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates, in general, to a photonics package incorporating a monolithically integrated alignment device for coupling optical energy between in-plane optical devices and to a method for producing the same. More specifically, the invention relates to a photonics package that incorporates an optical coupling and alignment device having an integral fiber groove, lens aperture and monolithic aspheric lens.[0002]Data in optical communication systems is often transmitted in the form of optical signals through an optical fiber terminating in a photonics device such as a receiver, transponder, transceiver, or the like. The data is projected from an optical fiber, for example as a light beam, directed onto a photonic die where the data is received by a photodetector and converted to a corresponding radio frequency (RF) electrical signal. However, data can easily be lost due to improper alignment between the fiber and the photodetector or t...

AI Technical Summary

Benefits of technology

[0008]In greater detail, and in a preferred embodiment of the invention, the photonics package of the invention is formed by first fabricating a monolithic coupler, or alignment device from a substrate by a conventional etching process. The alignment device incorporates an integral fiber groove on its top surface, an integral aspheric lens, and an integral recessed receiver portion on its bottom surface for receiving a photonic die and for positioning it under the aspheric lens. In one form of the invention, the die includes a photodetector region which is located to receive an optical signal directed into the alignment device through an optical fiber placed in the fiber groove. The groove and fiber are generally parallel to the surface of the aspheric lens (i.e. they are “in-plane”), with the terminal end of the optical fiber extending out of the groove sufficiently to be located above the lens. In this first form of the invention, the end of the fiber is cut at an angle to redirect an optical signal, propagating axially in the fiber, out of the fiber in a direction substantially perpendicular to the fiber's axis. The fiber cut may be polished and a high reflectivity coating added. The fabrication of optical fibers having a forty-five degree angle cut and the location of such fibers in a v-groove is illustrated in U.S. Pat. No. 5,324,954, which is hereby incorporated herein by reference. In accordance with this form of the invention, the optical signal from the fiber is directed through, and is focused by, the aspheric lens and is received by the photodetector region on the precisely positioned photonic die. In a second form of the invention the photonic die may incorporate a light emitter, such as a vertical cavity surface emitting laser diode (VCSEL) or surface light emitting diode (SLED), aligned with the aspheric lens for directing light signals into the optical fiber by way of the angled terminal end of the fiber. The integration of the various components of the alignment device provides for an easy-to-align, very small optical connector with reduced complexity and reduced manufacturing costs.

[0010]A final step for fabricating the alignment device includes metalizing the fiber groove and the bottom of the substrate block, as with solder. Thereafter, an optical fiber having an angled terminal end is secured in the groove with the optical axis of the angled surface of the fiber aligned with the optical axis of the lens, and a photonic die is positioned in the recess so that a photodetector region or a surface light emitting active area on the die is aligned with the optical axis of the lens, and thus with the optical signal axis of the fiber. The monolithic alignment structure assures accurate and reliable alignment of the optical fiber, the lens, and the photodetector or surface light emitting device, and lends itself to automatic assembly procedures.

[0011]Overall, the ability to form a monolithic, compact and simple optical coupling system for micro-optical devices has several advantages. For example, constructing all the components of an alignment device from identical material in a single process lowers assembly costs, reduces alignment problems during assembly and overcomes problems caused in earlier devices by unequal thermal expansion between components. Moreover, complex coupling and alignment schemes can be eliminated, reducing the number of components and the complexity of the process of manufacturing the device. A monolithic structure also permits a closer proximity of the fiber, lens, and photodetector light emitters, which allows for more accurate alignment, a decrease in the time required for alignment, and more efficient packaging of optical electronics systems. The assembly of the package can be automated, resulting in higher volume manufacturing and higher reproducibility.

[0012]In summary, a monolithic micro-optical device incorporating a photonics package in accordance with the present invention efficiently addresses various problems associated with optical communication applications and improves upon the prior art by providing a commercially advantageous product. The device eliminates the need for manual assembly and improves reliability and accuracy by simplifying prior devices.

Problems solved by technology

However, data can easily be lost due to improper alignment between the fiber and the photodetector or through light divergence, although both the alignment and divergence problems can be minimized where the fiber and the photodetector are in close proximity or where a lens can be used to focus the optical signal.

In the first construction, wherein light is projected from fiber directly onto the photodetector, the photodetector and the fiber must be optically aligned in three mutually perpendicular planes ((x-y), (x-z), and (y-z)), which complicates the assembly process.

Moreover, such an arrangement can be problematic for high frequency data transfer because it requires a longer wire bonding or transmission line, and this reduces device performance at high frequency operation.

This design configuration also results in the optical input being perpendicular to the RF signal output, and this requires much more space in a module.

These performance and size issues make this approach commercially less desirable, and this is the disfavored, if not unacceptable, approach for many applications where it is advantageous to have the fiber input and RF output substantially coplanar.

However, there are several problems with this method.

Using a discrete mirror (an additional element needing alignment) introduces an indirect connection between the fiber and photodetector, causing difficulty during alignment, raising costs due to the need for a more precise construction, and reducing reliability.

Further, the three components; namely, the fiber, lens, and photodetector, have to be precisely located with respect to each other to ensure reliable coupling, and this is difficult to accomplish.

In each of the configurations discussed above, the photonic package consists of several independently fabricated micro-optical components, including an optical fiber, a photodetector, a mirror, a lens and and a substrate or microbench on which the components are assembled, as well as bonding materials to connect the components, and frequently all were assembled manually, which is not efficient.

Although automated assembly could be used, it fails to achieve the needed alignment precision.

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